Sequential display system with changing color order

ABSTRACT

To sequentially display pictures in a television signal, a first picture is separated into sets of red, green and blue segments, with each segment of each color interleaved with the segments of the other colors in a first sequence for display in that sequence. Each successive picture is likewise separated into sets of red, green and blue segments, which each segment of each color interleaved with the segments of the other colors in a shifted sequence for display in that sequence. Shifting the color sequence of the segments of each successive picture among the primary colors so at least the first and last segment of the occurrence of motion artifacts that manifest themselves as a color distortion at the leading and trailing edges of a moving object followed by a viewer&#39;s eye.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit, under 35 U.S.C. § 365 ofInternational Application PCT/US03/21040, filed Jul. 3, 2003, which waspublished in accordance with PCT Article 21(2) on Jun. 10, 2004 inEnglish and which claims the benefit of U.S. provisional patentapplication No. 60/427,859, filed Nov. 20, 2002.

TECHNICAL FIELD

This invention relates to a technique that reduces motion artifacts thatmanifest themselves in a sequential display system.

BACKGROUND ART

Present-day sequential display systems typically comprise a light sourcethat illuminates a light modulator that has the capability ofcontrolling the illumination of each of a plurality of picture elements(pixels) projected onto a display. A controller controls the lightmodulator in response to an input television signal so that the lightmodulator will display successive pictures in the television signal,each picture appearing during a corresponding picture interval. Thelength of the picture interval depends on the selected televisionstandard. The NTSC standard currently in use in the United Statesprescribes a picture interval of 1/60 second whereas certain Europeantelevision standards (e.g., PAL) prescribe a picture interval of 1/50second.

A typical sequential display system achieves a color display bysequentially projecting red, green, and blue light onto the lightmodulator during each picture interval. Many sequential display systemsutilize a motor-driven color wheel interposed in the light path of thelight modulator to accomplish this task. The color wheel has at leastone set of primary color windows (typically red, green and blue) so thatupon rotation of the color wheel, red, green, and blue light illuminatethe light modulator. (Most present day color wheels have multiple setsof primary color windows.) In practice, each color is broken up into aninteger number of segments, with the segments of each color interleavedwith the segments of the other colors in time, thereby shortening theinterval between colors to reduce the problem of color break up withmotion.

Separating the picture into sets of primary color segments usuallyincurs the disadvantage that a moving white object will suffer colordistortion (i.e., motion artifacts) at its leading and trailing edges.In each new picture, the leading edge will have the same primary colorsay red, while the trailing edge will always have another primary color,say green, as the preceding picture. Usually, this problem is slightlyreduced but not eliminated, by increasing the number of primary colorsegments per picture to minimize the visibility of the colors at theleading and trailing edges of the object. However, most sequentialdisplay systems limit the number of primary color segments per picture.

Thus, there is need for a technique for minimizing such motion artifactsin a sequential display system.

BRIEF SUMMARY OF THE INVENTION

Briefly, in accordance with the present principles, there is provided atechnique for displaying at least a first and a second picture insequence with reduced motion artifacts. The method commences byseparating the first picture into sets of first picture segments, eachset associated with a different primary color (e.g., red, green andblue). Thus, for example, the first picture is separated into an integernumber of red segments, green segments and blue segments. The red, greenand blue segments comprising the first picture are interleaved in afirst color sequence. The second picture is likewise separated into setsof segments, each set associated with a different primary color. Thesegments of the second picture are interleaved in a color sequencedifferent than the color sequence of the segments of the first pictureso at least the first and last segments of the second picture are eachof different color than the first and last segments, respectively, ofthe first picture. The segments of the first picture are displayed intheir color sequence followed by a display of the segments of the secondpicture in their color sequence. Shifting the color sequence of thesegments of each successive picture among the primary colors serves toreduce the occurrence of motion artifacts that manifest themselves as acolor distortion at the leading and trailing edges of a moving objectfollowed by a viewer's eye.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a block schematic diagram of an exemplary sequentialcolor display system for illustrating the present principles;

FIG. 2 depicts a first embodiment of a color wheel in accordance withthe present principles for use in the display system of FIG. 1; and

FIG. 3 depicts a second embodiment of a color wheel in accordance withthe present principles for use in the display system of FIG. 1.

DETAILED DESCRIPTION

FIG. 1 depicts an exemplary sequential color display system 10comprising a light source 12 for generating a light beam 14 directedthrough a rotating color wheel 16 having at least three separate primarycolor windows 17, e.g., at least one red (R), one green (G) and one blue(B) window. A typical color wheel of according to the prior art has twored, two blue and two green windows interleaved in an RGBRGB sequence.During rotation of the color wheel 16, red, green and blue lightsuccessively strike the surface of a light modulator 18 for reflectionthereby onto a display screen 20.

A controller 22 controls the operation of the light modulator 18 inaccordance with an input television signal containing a sequence ofpictures, each picture appearing within a picture interval establishedin accordance with a prescribed television standard (i.e., 1/60 secondfor NTSC and 1/50 second for PAL). For each picture, the controller 22produces control signals causing the light modulator 18 to “generate”sets of picture segments with each set of segments associated with oneof the three primary colors (red, green and blue, respectively). Thelight modulator 18 generates a picture segment by reflecting light (ornot reflecting light) from the light source 12, as colored by the colorwheel 16, during an interval corresponding to the duration of thesegment. In the illustrated embodiment, the controller 22 causes thelight modulator 18 to generate four segments for each primary color, fora total of twelve segments per picture (four red, four green and fourblue). In practice, the color wheel 16 rotates at an integer number ofrevolutions during each picture interval, causing each of the segmentsassociated with each primary color to become interleaved with thesegments associated with each of the other colors in a color sequencethat remains the same from picture to picture.

In response to the control signals from the controller 22, the lightmodulator 18 selectively reflects the primary color associated with eachsegment onto the display screen 20 such that the individual pictureelements (pixels) in that color have an illumination intensity inaccordance with the incoming picture. The primary colors modulated bythe light modulator 18 appear in sequence on the display screen 20 toyield a color picture during each picture interval. The sequence ofcolors corresponds to the color sequence imparted by the rotating colorwheel 16. The display system 10 can include one or more lenses, mirrorsand/or prisms (not shown) to alter the characteristics of the lightstriking the light modulator 18 as well as to alter the characteristicsof the light displayed on the display screen 20.

In the illustrated embodiment, the light modulator 18 operates toselectively reflect incident light and thus the light modulator cancomprise a digital micromirror device (DMD), such as the DMDmanufactured by Texas Instruments. Although not depicted in FIG. 1, thelight modulator could take the form of a light transmissive device, suchas a liquid crystal, for selectively modulating the light fortransmission therethrough and onto the display screen. As will beappreciated, the properties of the light modulator 18 are not criticalto the present principles.

Present day sequential color display systems, such as system 10described above, display a moving white object with color distortion atits leading and trailing edges. In practice, the leading edge of such anobject will have a first color say red, while the trailing edge willhave a different color, say blue. This causes a motion artifact toappear as a viewer's eye tries to follow the moving object. Currently,present day sequential color display systems attempt to ameliorate thistype of motion artifact by increasing the number of segments per pictureinterval although many systems limit the number of segments.

In accordance with the present principles, the occurrence of colordistortion at the leading and trailing edges of a moving white objectcan be reduced by interchanging the sequence of the primary colorsimparted to the light striking the light modulator 18 so that at leastthe first and last segments of each successive picture have a differentprimary color than the first and last segments, respectively, of thepreceding picture. In the illustrated embodiment, interchanging thecolor sequence is accomplished by altering the arrangement of the colorwindows in the color wheel as well as changing the speed at which thecolor wheel rotates. FIG. 2 depicts a color wheel 16′ in accordance witha first preferred embodiment of the invention for interchanging thecolor sequence. The color wheel 16′ has nine color windows 17, with eachwindow having an arc of 40°. As compared to the color wheel 16 of FIG.1, the color windows 17 in the wheel 16′ are arranged in a GBBRGGBRRorientation, starting with the window 17 closest to the 12 O'clockposition and proceeding clockwise.

Assuming that a first picture starts with the upper left red window 17(i.e., the red window at the 10 O'clock position in the color wheel 16′of FIG. 2), the color sequence imparted to the light striking the lightmodulator 18 of FIG. 1 becomes RGBBRGGBRRGB upon counter-clockwiserotation of the wheel. The color wheel 16′ rotates at a non-integernumber of revolutions during each picture interval. In the preferredembodiment, the color wheel 16′ rotates 1⅓ revolutions per pictureinterval to establish four red, four green and four blue segmentsinterleaved in a first color sequence. For the next successive picture,the color sequence of the interleaved segments will shift by one color.For example, assume that a first picture has a first segment that is redand a last segment that is blue. A second successive picture will have afirst segment that is blue and a last segment that is green. A thirdsuccessive picture will have a first segment that is green and a lastsegment that is red. Thus, the arrangement of the color windows 17 inthe color wheel 16′, in combination with the non-integer number of colorwheel rotations per picture interval, causes the color sequence ofinterleaved segments to shift by one color from picture to picture.

Shifting the color sequence of the interleaved segments by one colorfrom picture to successive picture serves to reduce motion artifactsassociated with color distortion of the type described above. As the aviewer's eye follows a moving object, the color of imparted to the firstsegment of a picture appears as the color of the leading edge of theobject because each subsequent segment imprints on the viewer's retinain a location that lags the previously imprinted location. By shiftingthe color sequence imparted to first segment of each successive newpicture, the color of the leading edge of the moving object shifts amongred, blue, and green at one-third the picture frequency. Thus theleading edge will tend to have the same color as the original object,thereby virtually eliminating the problem of color distortion.

FIG. 3 shows an alternative embodiment 16″ of a color wheel inaccordance with the present principles, which when rotated at anon-integer number of revolutions, effects a one-color shift in thecolor sequence of the interleaved segments for each successive picture.As seen in FIG. 3, the color wheel 16″ comprises three red, three greenand three blue color windows 17, each having an arc of 40° and arrangedin a RGBGBRBRG sequence, commencing with the red window closest to the12 O'clock position and proceeding clockwise. In operation, the colorwheel 16″, when substituted for the color wheel 16 of FIG. 1 and rotatedat 1⅓ rotations per picture interval, will accomplish a one-color shiftin the color sequence of the interleaved segments of each successivepicture in a manner comparable to the color wheel 16′ of FIG. 2. Ascompared to the color wheel 16″ of FIG. 2, the color wheel 16′ affordsthe advantage of fewer “spokes” (i.e., transitions between colors). Thereduced number of spokes in the color wheel 16′ of FIG. 2, as comparedto the color wheel 16″ of FIG. 3, allows for more economical coding ofthe segments when the light modulator 18 is operated by pulse widthmodulation.

Other mechanisms besides the color wheels 16′ and 16″ of FIGS. 2 and 3,respectively, can interchange the sequence of primary colors imparted tothe interleaved segments of each successive picture to reduce the motionartifacts associated with color distortion. For example, there existmechanisms such as liquid crystal displays and the like whichsequentially impart each of three primary colors to the light incidenton the light modulator 18. The operation of such mechanisms can bealtered in accordance with the present principles to sequentially thecolor sequence imparted to the interleaved segments by one color foreach successive picture in the same manner as the color wheels 16′ and16″.

It is possible to shift the color sequence imparted to the interleavedsegments of each successive picture by one color using a conventionalcolor wheel, such as the color wheel 16 of FIG. 1 rotating at an integernumber of revolutions per picture. Simply dropping a different colorsegment for each successive picture will cause a shift in the colorsequence by one color so that the first and last frames of eachsuccessive picture will have a different color than the first and lastframes, respectively, of a previous picture. Dropping a different colorsegment per picture however will cause a loss in picture brightness.Therefore, this approach to shifting the color sequence likely will notprove as efficacious as using either of the color wheels 16′ or 16″ androtating each wheel a non-integer number of rotations during eachpicture interval.

It is also possible to shift the color sequence of the segments of eachsuccessive picture by one color using a conventional color wheel withoutany loss of brightness. Such shifting can be accomplished by simplyseparating the picture into an unequal number of segments, say four red,four blue and three green. The effect of having an unequal number ofsegments will cause an inherent shift in the color sequence for each newpicture. Unfortunately, having such an unequal number of segmentsrequires very sophisticated memory management within the controller 22,rendering this approach impractical.

The foregoing describes a display technique that affords reduced motionartifacts to the human eye following a moving object.

1. A method for displaying at least first and second incoming picturesin sequence, comprising the steps of: separating the first picture intosets of first picture segments, each set associated with a differentprimary color; interleaving the first picture segments in a first colorsequence; separating the second picture into sets of second picturesegments, each set associated with a different primary color;interleaving the second picture segments in a second color sequence inwhich at least the first and last second picture segments are each ofdifferent color than the first and last first picture segments,respectively, and sequentially displaying the first picture segments inthe first color sequence; and thereafter sequentially displaying thesecond picture segments in the second color sequence.
 2. The methodaccording to claim 1 wherein the second color sequence is shifted by oneprimary color from the first color sequence.
 3. The method according toclaim 1 wherein the step of separating the first picture includes thestep of imparting to each of the sets of first picture segments adifferent one of a red, green and blue primary colors.
 4. The methodaccording to claim 1 wherein the step of separating the second pictureincludes the step of imparting to each of the sets of second picturesegments a different one of a red, green and blue primary colors.
 5. Themethod according to claim 1 wherein the step of separating the firstpicture into sets of first picture elements includes the step ofdropping a segment of a primary color and wherein the step of separatingthe second picture into sets second picture elements includes dropping asegment of a different primary color than the segment dropped for thefirst picture.
 6. The method according to claim 1 wherein at least oneset of first picture segments associated with a primary color has adifferent number of segments than a set of first picture segmentsassociated with a different primary color and wherein at least one setof second picture segments associated with a primary color has adifferent number of segments than a set of second picture segmentsassociated with a different primary color.
 7. A method for successivelydisplaying color pictures such that each picture appears during apicture interval, comprising the steps of: separating each successivepicture into sets of segments, the number of sets of segmentscorresponding to a prescribed number of primary colors; imparting eachof the primary colors in a prescribed sequence to a beam of lightdirected onto a light modulator, said each primary color impartedsimultaneously with the application of a control signal to the lightmodulator causing the light modulator to modulate the segment of theprimary color for display on a display screen; and changing the sequenceof primary colors imparted to the light directed onto the lightmodulator upon each next successive picture so that the primary colorassociated with at least a first and a last segment of said each nextsuccessive picture differs from the primary color associated with eachof the first and last segments, respectively, of a preceding picture. 8.The method according to claim 7 wherein the imparting step comprises thesteps of: interposing a color wheel having a plurality of red, greed andblue interleaved color windows in the beam of light striking the lightmodulator so that the beam of light will pass through a color window andonto the light modulator; rotating the color wheel at a non-integernumber of revolutions per picture interval to impart a prescribedsequence of red, green and blue colors to the light directed onto thelight modulator.
 9. The method according to claim 7 wherein the changingstep includes the step of arranging the color windows in the color wheelsuch that as the wheel rotates, the sequence of red green and bluecolors imparted to the light beam striking the light modulator changesfor each picture.
 10. A sequential color display system for displayingsuccessive pictures, comprising: a light source for producing a lightbeam; a light modulator lying within the optical path of the light beamfor modulating the light beam onto a display screen; means forseparating each successive picture into sets of segments, the number ofsets of segments corresponding to a prescribed number of primary colors,and for applying control signals to a light modulator to cause the lightmodulator to generate said sets of segments such that each segment of aset is interleaved between segments of other sets; a color sequencingmechanism interposed between the light source and the light modulatorfor imparting to the light beam each of the primary colors in aprescribed sequence, said each primary color imparted simultaneouslywith the application of said each segment to the modulator, the colorsequencing mechanism changing the sequence of primary colors imparted tothe light directed onto the light modulator upon each next successivepicture so that the primary color associated with at least a first and alast segment of said each next successive picture each differs from theprimary color associated with each of the first and last segments,respectively, of a preceding picture.
 11. The system according to claim10 wherein the color sequencing mechanism comprises a color wheel havinga plurality of color windows arranged to impart a separate one of a red,a green and a blue color to the light directed onto the light modulatorupon rotation at a non-integer number of rotations per picture interval.